1. Field of the Invention
The present invention relates to the recovery of oil and, more particularly, to a system for the treatment and extraction of crude oil from subterranean oil formations.
2. Description of the Prior Art
It is well known that most oil recovery techniques recover only a small portion of the actual oil present in a given oil-bearing formation. For this reason there is a great deal of interest in developing techniques which permit the recovery of the remaining quantities of oil. Generally, these techniques utilize various flushing or pressurizing methods which augment the oil formation pressure through one or more injection wells within a reasonable proximity to one or more producing wells.
The flushing or pressurizing fluids may take the form of steam, hot gas, water, water with surface active, thickening or other agents, carbon dioxide and various types of solvent solutions. One purpose for injecting such fluids is to reduce the surface tension of the tightly-bound oil adhering to the particles of the oil-bearing structure. Another purpose is to merely flush out or displace the oil between the formation pores. The injection of gas or other fluids alone, however, is usually only partially effective. Also, such injection fluids are relatively expensive and require facilities for preparation and/or transportation to the oil field. Additionally, prior art injection systems require extensive pressurization and/or injection equipment. Only water alone is practical on a widespread basis, and its ability to increase yield is low. Other methods are either not, or only marginally economical at the present time.
One of the more potentially productive oil recovery processes is to use "miscible" fluids. U.S. Pat. No. 2,412,765 describes the injection of light hydrocarbons comprising mainly propane and butane into depleted oil reservoirs at the reservoir pressure. Similarly, U.S. Pat. Nos. 2,297,832 and 2,724,438; 2,880,801 and 3,223,157 disclose processes treating oil formations with residue gases and hydrocarbons, which may be flashed from the recovered crude oil or purchased from outside sources.
Each of the above patents, however, suffer from the disadvantage that the light hydrocarbons have a tendency to channel and short-circuit through the formation rather than becoming inimately mixed with the crude oil present. The purchase of the light hydrocarbons is also very expensive, and most oil fields, especially depleted ones, have very little light hydrocarbons in the oil. Additionally, the injection of such light hydrocarbons generally requires the addition of expensive storage and compression equipment to effect injection to the reservoir.
As a means for reducing the purchase cost and perhaps diminishing the retentive forces holding the oil within the pores of the formation, two-stage injection processes have been developed such as that shown in U.S. Pat. Nos. 2,347,769, 2,609,051 and 3,780,808. The above patents utilize a hydrocarbon gas followed by an injection of gas or water. This reduces the amount of light hydrocarbons needed, but is very difficult to control, and seldom obtains much increase in oil production.
In the 3,780,808 patent, a water/hydrocarbon colloidal silica mixture, which is partially miscible with the formation oil, is injected to increase the viscosity of the flushing fluid, thus facilitating the flow of the formation oil into production wells. Numerous other patents also propose a similar use of additives to the water or oil.
It is clear that a major disadvantage of the above-described miscible fluid and other processes, resides in the high cost of the light hydrocarbons or the additives, transporting them to the oil field, including the provision for storage, water treatment and the necessity of powerful injection equipment. Additionally, none of the patentees contemplated the use of cracking equipment, operating at high pressure, located at the site for producing injection fluids and other desirable hydrocarbons from the formation's oil or by treating purchased inexpensive oil. Conventional crackers are so large, expensive, and complex to operate that it has never been considered possible to have them operate in the oil field area.